As an optical fiber splicing process, there has been known V-shaped groove splicing in which two lengths of optical fibers are connected in series by positioning optical fibers in a V-shaped groove of a substrate to butt them at their ends and then bonding them by fusion. In such a process, it is a serious problem how to prevent an excess stress acting on the optical fibers to be spliced. Since the optical fibers are easily damaged by an excess tensile force, bending or torsion, it is required to introduce the optical fibers into the groove of the substrate so that they have a curvature as large as possible.
For this end, there have been so far proposed to use various types of optical fiber holders, which are arranged opposite sides of the substrate to hold each optical fiber at the most bent portion of the optical fiber to be spliced so that each optical fiber is movable in the axial direction. One of the known optical fiber holder, comprises, as shown in FIG. 4, plural pairs of fixed pins 20 and movable pins 22 so arranged that they are facing each other in parallel, said movable pins 22 being fixed to a movable plate 19 forced upwardly by a spring 21. In this holder, an optical fiber 30 to be spliced is put between the fixed pins 20 and movable pins 22 to hold it by the frictional force between the optical fiber 30 and pins 20, 22. However, it is impossible with this holder to hold the optical fiber under a constant holding force since the frictional resistance between the optical fiber and the pins varies with surface conditions of the optical fiber and conditions of the open air. If the frictional forces between the fiber and pins are increased by oil or dust stain on the optical fiber, it occasionally obstructs smooth movement of the optical fiber in its axial direction, resulting in breakage of the optical fiber by a large tensile or bending force acting thereon.
Another optical fiber holder comprises, as shown in FIGS. 5 and 6, a holding guide 23 put between a main body 24 and a push plate 26 forced upwardly by a spring 25. In use, an optical fiber 30 is inserted into the guide member 23 held between the main body 24 and push plate 26 by the frictional force between them. If the holder is used under inclined conditions, the guide member 23 receives a force causing its sliding movement under the influence of gravity. For this reason, the axial force varies with the inclination angle of the holder, thus making it difficult to hold the optical fibers under the predetermined constant holding force so that they are movable in the axial direction.